Pension fund boards must decide how to invest on behalf of millions of members, including when investment choices involve trade-offs between financial returns and social impact. Making these decisions well requires boards to understand their members’ considered social preferences. We introduce deliberative democracy tools as a method for eliciting these preferences. Deliberation exposes members to balanced expert information, creates structured opportunities for peer exchange, and helps members work through complex trade-offs before expressing their views. Partnering with a large Dutch pension fund, we conduct two field experiments that combine a deliberative mini-public with a binding maxi-public vote. In the mini-public, 49 randomly selected members participate in a three-day, in-person process of structured peer deliberation and balanced expert briefings on sustainable investing. After deliberation, participants formulate and vote on recommendations for the pension board. Deliberation does not change how much financial return members are willing to sacrifice for sustainable investing. What changes is how members approach the trade-off. As knowledge increases, non-consequentialist views fall from 34.9% to 9.3% and consequentialist views rise from 20.9% to 44.2%. Mini-public members produce several recommendations for the pension board, among which expanding impact investing features prominently. To test whether this reflects the broader membership, the board puts the impact investing question to a binding vote. A total of 13,619 members participate, choosing between stopping, maintaining, or expanding impact investing, with the explicit understanding that the outcome determines actual portfolio allocations. We communicate that impact investing can reduce pension payments at retirement, but may also have positive environmental and social impacts. Despite this financial trade-off, a clear majority favors expansion over stopping. The mini-maxi-public translates considered social preferences into consequential investment decisions: the board commits to increasing impact investments from 300 million to 1.2 billion euros.
